1. Field of the Invention
This invention relates to the field of power transmission for use in mechanized agricultural equipment, and more particularly to an adjustable coupler for coupling an in-line drive shaft to the wheel drive gearboxes that drive the wheels supporting and propelling an agricultural irrigation system.
2. Description of the Prior Art
Center pivot and linear irrigation systems are utilized to irrigate large sections of land. Typically, such systems are capable of watering a quarter section of land, i.e., 160 acres, or more. A center pivot irrigation system is an approximately one-quarter mile mechanized pipe that rotates around a fixed pivot point. When activated, the irrigation pipe rotates around the pivot, emitting liquids over the area. The length of time required for a 360-degree rotation of the irrigation pipe typically range from 12 hours up to several days. Linear irrigation systems are comprised of similar irrigation structure, but move linearly across sections of land to be irrigated, typically by wire guidance.
In conventional irrigation systems, the irrigation pipe spans are 120- to 180-foot lengths supported by a wheeled tower at each intersecting span. Sprinklers are located at spaced intervals either along the length of the span or along a water conduit parallel to the span. The wheels of each tower are normally positioned perpendicular to the span such that the system moves laterally. When constructed, wheels tracks are established to follow a prescribed path, either circular for center pivot systems or linear for linear systems. Each tower is typically provided with one or more drive motors operable to move the tower. Generally, power from the motors is transferred through a gearbox to the wheels. Most conventional systems either utilize an electric gearmotor mechanically connected between the pair of wheel drive gearboxes, or hydraulic or electric motors directly coupled to the wheel drive gearboxes. Typically, the drive motors have a round output shaft that is coupled to a square drive shaft of the wheel drive gearbox. In the agricultural industry, these square in-line drive shafts generally range from ¾″ to 1″ square.
As with other components of agricultural equipment, the couplers utilized to inter-connect the square drive shaft with the round output shaft are often subject to extreme operating conditions and environments. For example, common in such environments are hazards such as moisture, corrosive liquids including liquidized manure, the full range of soil and mineral conditions, insects and temperature extremes which could range from continental polar to equatorial. Likewise, because the terrain on which agricultural irrigation systems operate is often rocky, uneven and has varying surface conditions, such couplers are subject to high torque.
The standard prior art coupler consists of a rubber dampening puck sandwiched between two, two-piece collars. The dampening puck absorbs shock that could be transferred between the two collars and permits a degree of flexibility between the interconnected drive shafts. One collar is disposed to fit around the round cross-section end of the output shaft of the drive motor while the other collar is disposed to fit around the square cross-sectioned end of the drive shaft. Each collar may have a flange that permits it to be bolted or attached to the flange of the other collar, with the dampening puck disposed between the adjacent flanges. Alternatively, each collar may have teeth or similar interlocking protrusions that permit it to engage corresponding structure on the adjacent collar, again with the dampening puck clasped between the two collars. As mentioned above, the dampening puck is generally formed of rubber or other shock absorbing material such as polyurethane. The collars are generally formed of aluminum cast to fit the specific drive shaft size and shape.
One drawback to these prior art couplers is that they do not allow flexibility in the field for different drive shaft sizes. Specifically, these couplers are cast to fit around a specific size gearbox drive shaft, and are not configured to fit around drive shafts of similar shape but with different dimensions. Another drawback of the prior art couplers is their inability to handle the torque capacity of high performance drive systems. Generally, the tensile strength of aluminum is inadequate to meet the high torque applications required of such systems. Finally, these prior art couplers often erode and fail due to hazardous environment in which they are used. Abrasive materials such as sand, dirt, chemicals, etc. migrate between the aluminum collars and the puck, causing erosion of the coupling components. This problem is particularly acute in couplers where the collars have a large surface area in contact with the puck, such as those collars having a large base or flange for attachment to the puck. Those skilled in the art will understand that as the puck flexes and bends, pockets are created between the puck and flanges, enhancing the opportunity for contaminants to become trapped between components and thereby causing erosion of the components. This erosion is further exacerbated by the cyclic operation of the system and the various stresses placed on the components through operation of the equipment.
Various attempts have been made to address some of these drawbacks, the most noteworthy of which is found in U.S. Pat. No. 5,678,772. This patent teaches a universal coupler for in-line coupling drive shafts together in a motor driven irrigation system. Specifically, the coupler includes a first receptacle for mounting on the end of a motor output shaft, wherein the receptacle has an elongated base portion that attaches to a flexible, shock absorbing puck attached. Attached to the opposite side of the puck is a V-shaped cradle structure formed of elongated flat walls extending axially from said puck. This cradle also has an elongated base portion that permits the cradle to be attached to the puck in the x-axis. Furthermore, each wall has an elongated slot positioned to be perpendicular to the slot in the adjacent wall. The slots are disposed to receive an angle bolt such that when secured in the slot, the legs of the bolt and the walls of the V-shaped cradle form right angles to one another for securing about the square drive shaft of a gearbox. While the angle bolts are adjustable in the elongated slots to permit the coupler to be attached to varying size square drive shafts, a major drawback of the coupler is the lack of symmetry which results in unbalanced forces being placed on the disk, thereby leading to early failure. The V-shaped cradle is fixed in place on the puck, while only the angle bolts are adjustable. Because of this, while the round motor output shaft, puck, first receptacle and V-shaped cradle are all co-axial, the square drive-shaft mounted in the V-shaped cradle is off-center, resulting in undesirable forces generated through the puck and hardware. As mentioned above, one of the drawbacks in prior art couplers is their inadequate torque capacity for high performance systems. In addition, the V-shaped cradle is attached to the disk along only a single axis, such that any forces placed on the cradle, and hence the disk, are concentrated along the single axis, creating a concentrated bending plane through the axis.
Thus, it would be desirable to provide an adjustable coupler that minimizes off-balance forces during operation. Such a coupler should also minimize surface area contact between the components to reduce the opportunity for contaminants to erode the coupler components.